In a hydraulically actuated electronically controlled unit injector, spool valves may be used to control a flow of high-pressure hydraulic fluid to an intensifier chamber. The hydraulic fluid is directed into the intensifier chamber in a timed sequence to operate a piston in the injector body. The high-pressure hydraulic fluid is provided from an inlet chamber of the injector to the intensifier chamber through the spool valve when the spool valve is open. The fluid within the intensifier chamber presses the piston against the bias of a piston spring. When the spool valve is closed, the high-pressure hydraulic fluid within the inlet chamber is cut off from the intensifier chamber. Also, closing the spool valve places the intensifier chamber in fluid communication with an outlet passage of the injector, thereby allowing the hydraulic fluid to exit.
Spool valves have a spool that reciprocates inside the body of the injector. In the open position, the spool valve is moved to a location to form a fluid flow path between the inlet chamber and intensifier chamber while closing off flow from the intensifier chamber to the outlet passage. In the closed position, the spool valve is moved to a further location to form a fluid flow path between the intensifier chamber and the outlet passage while preventing flow of the high-pressure hydraulic fluid from the inlet chamber to the intensifier chamber.
The fluid flow paths created by the spool valve may have sharp edges defined by its grooves and lands. Over time, however, such edges may become worn, abrupt, and/or jagged caused by damage from debris or cavitation. In such instances leakage of the high-pressure hydraulic fluid may occur as it flows through the spool valve, rendering the injector defective and unsuitable for use.